chriswit1

Hey Guys, I have a 99 996 Carrera with Tiptronic, almost 40,000 miles.

The car has been perfect until recently... I always drive the car in Automatic, and never shift with the Tip buttons. Also, I have always driven the car very mildly. But I finally, recently, started to drive the car hard, floor it all the way, and not baby it so much and I fear I have damaged the transmission...
This is whats happening... The car shifts fine 1,2,3... But sticks in 3rd... even when i take the rpms all the way up it, it seems that it stays in 3rd... So, I have to now use the tip buttons to shift past 3rd.... 4th 5th.... etc. In Manual Tip mode the shifts are quick and sound perfect... Only while in automatic does it stay in 3rd... Also, every once in a while it will start to shift normally, but it never lasts long...
-Anyone had this issue... Is there a computer that sends the shift signal that can go bad... or a speed sensor or something that is a diy fix... I am low on funds and not near any close Porsche dealers or mechanics... And lastly, since the car seems to be flawless in Manual Tip, will driving it any further hurt anything if I just use manual, since the issue seems to only be while in automatic???
-- Any Input would help...

Thanks Much!

Jacks911

Driving the car in Tip Manual should not cause any harm. But likely you have either and electrical gremlin - ground issue or as you guessed a sensor is intermittent. The Tip brain should give a fault if there are issues so any Porsche specialist should be able to read the fault code and estimate the trouble shooting plan. If it is the Brain it will be expensive. The Tip electronics will protect the transmission if there is a serious fault by going into Limp home mode - basically stuck in 3rd gear I believe. But it should then stay in 3rd when you come to a stop and drive off again. I suppose you could have some intermittent failure causing this lock in 3rd, but it is then OK when you start again. Hope it is just a ground issue and an easy fix.

chriswit1

Thanks for the response, I drove the car all night last night in Manual, and it was fine... then this morning, I tried it again in auto, and the same thing... goes up 1,2,3, normal and stays in 3rd gear no matter how high the rps go up... It goes back down when i stop, and will still downshift if i floor it... So I will have to take it in like you suggest... My luck it will definitely be the Brain...

- on a good note, I am really liking driving the car in manual, and its also funny that I never drove it that way because I thought it would hurt the tranny, and the tranny screwed up anyway... lol

Torontoworker

An educated guess here; That model TIP (same as mine) has it's torque converter and control module (TCU) on the inside of the case. You may be having issues with the electrical actuators for the third gear solenoid. The bad part is that you have to drop this transmission (Merc made) to get to it. The up side is that using the manual mode bypasses the need for some of the switching operations that are used while in auto.

You need to take care of this transmission, these things are expensive and issues like this don't get better and can get a lot worse down the road. It's cheaper to get it serviced - check the fluid to see if it is overdue for a change or if it is low. The fluid is expensive - seems to have come out of the shuttle program and made from liquid platinum! (Just kidding) A minimum charge at a dealer for fluid change and diagnostic is $1000. Replacement is above $9K - rebuilds about half that.

One thing you can do right now that may give a mechanic a better idea of what has gone wrong is to get someone with Durametric software and an OB2 cable to plug in and read the codes from the transmission. There should be a code or two sitting in memory. If you were having random issues and in different gears - you could figure TCU or electrical harness issues but a single gear and only in 3rd while in auto is almost generic with these models.

You don't have to take the car to Porsche dealer - ask around Mercedes dealers where they get their auto transmissions serviced and go there yourself and save money. No dealer outside of fluid changes or swapping the easy parts out opens up these transmissions - they are all sent out to specialist shops - save the dealer mark up. Good luck.

Jacks911

I think Toronto is wrong about the tranny manufacturer in your 996. If your 996 is a MY99 it is NOT a Merc Tranny. They started in MY2002 with the 3.6 motors. The early 996's with 3.4 liter motors had ZF boxes with a simpler Tip controller with 5 shift program patterns. The Chrysler / Merc tranny had the 255 program Super Tip controller and a 2 speed reverse, 5 speed forward gearing. Same as the Turbo box.

chriswit1

Thanks, I definitely need to replace the trans fluid... My car has NEVER had it changed, I always thought that was something I would have to do when the mileage was higher. But I didn't take into account that the fluid deteriorates just based on the car being 13 years old... But I should wait, my luck I will change the fluid, and then the problem will be one that needs the trans opened up anyways... lol

And Jacks, my Trans does only have about different 5 modes, they are very distinct and I usually know what mode its in...

I am going into Woodlawn Auto today to have the codes read, and I will let you guys know what they find out. Its a cool shop, they always have racing porches in for service and I like checkin em out... : )

Thanks

Torontoworker

Correct - ZF. (However, found a reference to MY 2000 986/996's getting the Daimler-Chysler units but no reason given)

But the 'can't shift past 3rd gear' cannot be cured with just a fluid re-fresh. I checked with my indy today and he targeted an issue with the TCU as a start and then or check TQ operation.

ChristopherG

The switch that tells the transmission what position the shifter is in may be malfunctioning in auto mode. Tip being a different position on the shifter would not necessarily be affected by this problem. Check the other options before replacing the fluid on the ZF transmissions it's a pain to do. On the Audi ZF boxes i'm more familiar with the transmission temp needs to be monitored by computer and refilled in multiple steps.

Fluid is also around $35 a liter if I remember correctly.

chriswit1

Just had the codes read and there is no issues currently and no codes recorded in history.. . One of my wheels had wear on the inside ( metal showing ) and they would not test drive it themselves until the tires were replaced... I just got new wheels, and I will have the car back to Porsche for an alignment, and hopefully they will be able to experience the issue this time. Thanks for everyone's help so far, and I will keep troubleshooting until we figure it out. For now I have been driving in Manual all the time, and I like it... : v)

Torontoworker

Pentosin brand - $17.25ea at Pelican (But cheaper in volume) x 8-9 bottles for a full change.


The procedure is a pain in the butt to have to suck the stuff out but it's not that difficult. You can tell when the fluid is on it's last legs from the dark, dark brown color and the horrible smell.

chriswit1

Bizarre.... So I had the new wheels put on and the car aligned, and the Transmission is 100%...
my rear right wheel was bent way out of whack, and it literally was shredding the tire on the inside... I saw the tire and you could see through 3 layers of metal... It was the only tire that was getting worn...
The tech said he never saw a tire this bad that haddent blown in his career.... Lol....
But, that was the cause of the tranny issue. I don't see how the 1 out of whack wheel tripped out the trans, but it did.... and as the tire got worse and worse the issue got worse and worse... Bizarre, but so Glad the Trans is back shifting all smooth and nice!....

Thanks for everyone's input and help with this... And I am still going to have the fluid and filter changed as you suggest to avoid any Future problems as its a 99 and still has the original fluid....

Pac996

strange

vwillo1

I know that this thread is old, but, if you have PASM (stability management) uneven or excessive tire wear on one or more corners will cause issues.